View Full Version : JBL 123a experts.....


onemug
01-12-2011, 04:19 PM
Backstory:

I have a pair of Valencia cabinets that have a JBL 123a woofer in them (2" dome mid and 1" dome tweeter if interested). The midrange and x/o are brand new so I have been playing music thru them for about a month now enjoying them more and more as the mid loosens up. What I remember about these specific JBL's are: white, 12", pro series and alnico magnets.

Questions are:

1. I have used several different types of amps on these while the mid was breaking in and it seems the JBL needs a really strong amp to get the best out of it. Is this because of the strength of alnico magnets?

2. What are the differences between a 123a-1 and 123a-3?

I'm impressed with the bass that these put out in these cabinets, both the amount and resolution. Any info would be appreciated.

jlovda
01-12-2011, 04:55 PM
JBL speakers in general are very efficient. In fact I read at the Lansing Heritage site that Jim Lansing pushed efficiency rather than bass. Way back when Thiele-Small simulations just got started, I measured the parameters of an 123a and LE14a woofer. I could not get a box and port combination that produced flat low frequency response. The 123a's always were underdamped with a bump. The LE14a's were always over damped and rolled off prematurely. I do not think any JBL speakers were designed using Thiele-Small parameters until the mid-80's (my guess). But they were efficient!

onemug
01-12-2011, 11:47 PM
JBL speakers in general are very efficient. In fact I read at the Lansing Heritage site that Jim Lansing pushed efficiency rather than bass. Way back when Thiele-Small simulations just got started, I measured the parameters of an 123a and LE14a woofer. I could not get a box and port combination that produced flat low frequency response. The 123a's always were underdamped with a bump. The LE14a's were always over damped and rolled off prematurely. I do not think any JBL speakers were designed using Thiele-Small parameters until the mid-80's (my guess). But they were efficient!


Thanks for the info.